1. Field of the Invention
The present invention relates to a distributed directory system to manage servers by distributing information about contents transmitted from many terminals and provide, when a request for information search is made from the terminals, managed information to servers.
2. Description of the Related Art
Recently, in mobile terminals such as a mobile phone, PDA (Personal Digital Assistant), vehicle-mounted terminal, and the like, demands for exchanging, while moving, through a network, a large volume of contents such as voices and videos are being spread among users.
Further, there are also demands for making information generated by street monitoring cameras and/or various sensors be circulated together through a network to make the most use of the information.
Technologies to meet such demands are being studied and, especially, in a state where a large volume of various contents are distributed, it becomes important to deliver information about contents without impairing freshness of contents.
As directory technology supporting the circulation of contents over the current Internet, a P2P being a periodical information collecting means and a distributed management means by using a search robot being a non-management means.
In the periodical information collecting means using a search robot, as disclosed in Non-patent reference 1 (Yoshihiko Hayashi, Yoshitugu Kohashi, “Technological movement of search service on the web site” and “Information processing” Vol. 39 No. 9 p-861-865, September 1998), a search robot called a crawler circulates to collect contents being scattered in servers over the network intensively in an index server to arrange and provide contents information to users.
In the P2P means, as disclosed, for example, in Non-patent reference 2 (Eng Keong Lua, Jon Crowcroft, Marcelo Pias, Ravi Sharma and Steven Lim, “A survey and Comparison of Peer-to-Peer Overlay Network Schemes, IEEE COMMUNICATIONS SURVEY AND TUTORLAL, March 2004), an overlay network is constructed by a user machine participating in the P2P and an index of entire contents information is divided to specify a place where contents information exists in order to provide the same to users.
However, such conventional means as disclosed in the Non-patent references 1 and 2 cannot keep up with a state of frequent production, change, disappearance of technologies in a ubiquitous network society.
For example, in the periodical information collecting means using the search robot, in order to follow frequent updating of contents, it is necessary for many crawlers to frequently circulate in a network, thus requiring huge processes and costs for maintaining serves.
Moreover, in the P2P serving as the distributed management means, lots of servers have to be prepared to provide all contents to all persons who want to have information.